<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>]
    <h4>debugger关键字:</h4>
    <h4>打开调试器后，下面的代码应在执行第三行之前停止执行：</h4>
    <h4>按F12打开然后刷新页面</h4>
    <p id="output"></p>
    <script>
        var a = 50 + 20;
        debugger;
        document.getElementById("output").innerHTML = a;
    </script>
</body>

</html>